Mizuki "just left you here", huh? Inflating and everything? Yeah, right! I bet you snuck into her dimension to try out her new pump! So how about I go and make this overinflated state of yours permanent, huh? If Mizuki really did know you were here, she'll be able to change it back.

When Mizuki did end up coming back, she laughed for a solid minute at the misunderstanding, and proceeded to keep the transformation permanent anyway.